code: def nulldf_strategy():
      return data_frames(
          columns=[
              column(
                  "1", st.floats(allow_nan=True, allow_infinity=True)
              ),
              column("2", st.sampled_from([np.nan])),
              column("3", st.sampled_from([np.nan])),
          ],
          index=range_indexes(min_size=3, max_size=20),
      )
  
file_path: pyjanitor/janitor/testing_utils/strategies.py
imports: import numpy
  from hypothesis import strategies
  from hypothesis.extra.pandas import column, data_frames, range_indexes, series
label_desc: Use image node_id 1 for calling a global function with example usage: nulldf_strategy() and returns: data_frames